I used to take FG readings using a plastic wine thief, but since I use the wine thief for my barrel aged sours I don't dare. Currently, I just guess-timate when the beer is done. Fortunately , over the past couple years I've acquaint myself with the behaviour of the same 5 yeast strains, and keeping with the same brewing and fermentation methods I've had luck estimating when the beer has reached FG. However, I'm curious to hear what approach my fellow brewers take with FG readings and fermenting in glass carboys?